At present the industrial automation level has
become the weight all the various trades and occupations modernization
level an important symbol. At the same time, the control theory
development has also experienced the classical control theory, the
modern control theory and the intelligent control theory three stages.
The intelligent control typical example is the fuzzy entire
automatic washer and so on. The automatic control system may
divide into the open-loop control system and the closed-loop control
system. A control system â–¡p changes the delivering â–¡p
implementing agency â–¡p input output connection including the
controller â–¡p sensor. The controller output â–¡o adds to after
the output connection â–¡p implementing agency is controlled on the
system â–¡r the control system to control the quantity â–¡o â–¡o to
change after the sensor delivering â–¡o to deliver through the input
connection the controller. Different control system â–¡o its
sensor â–¡p changes the delivering â–¡p implementing agency is
dissimilar. For instance the pressure control system must use
the pressure transmitter. The electric heating control system
sensor is the temperature sensor. At present, PID control and
its controller or intelligent PID controller (measuring appliance)
already very many, the product has been been actual in the project
obtained the widespread application, has various PID controller
product, each big company developed had the PID parameter from 整定
the function intelligent regulator (intelligent regulator), PID
controller parameter automatic control was through the
intellectualized adjustment or from the adjustment, the auto-adapted
algorithm realizes. Has uses the PID control realization the
pressure, the temperature, the current capacity, the fluid position
controller, can realize the PID control function programmable
controller (PLC), but also has may realize PID control PC system and
so on. The programmable controller (PLC) is uses its closed-loop
control module to realize the PID control, but the programmable
controller (PLC) may direct and ControlNet is connected, like Rockwell
PLC-5 and so on. Also has may realize the PID control function
controller, like the Rockwell Logix product series, it may be directly
connected with ControlNet, realizes its long-distance control function
using the network.
1st, open-loop control system
The open-loop control system (open-loop control system)
is refers is controlled the object the output (controls quantity)
(controller) the output not to affect to the controller. In this
kind of control system, will not rely on is controlled the quantity
instead to return to forms any closed loop return route.
2nd, closed-loop control system
Closed-loop control system (closed-loop control system)
the characteristic is the system is controlled the object the output
(to control quantity) to be able instead to return to affects the
controller the output, forms or many closed loops. The
closed-loop control system has the regeneration and the negative
feedback, if feedback signal and system given value signal opposite,
then is called the negative feedback (Negative Feedback), if the
polarity is same, then is called the regeneration, the general
closed-loop control system uses the negative feedback, also calls the
negative feedback control system. The closed-loop control system
example are very many. For instance the person is has the
negative feedback the closed-loop control system, the eye then is a
sensor, acts as the feedback, the human body system can finally make
each kind of correct movement through the unceasing revision. If
does not have the eye, did not have to feed back the return route,
also has become a open-loop control system. Another example,
when a genuine entire automatic washer has can continuously inspect
the clothing whether cleans, and after cleaning can the automatic
turnoff power source, it be a closed-loop control system.
3rd, step leap response
The step leap response is refers when (step function)
adds to a step leap input on the system, system output. After
the static error is refers to the system the response to enter the
stable state â–¡o the system difference of expectation output and the
actual output. The control system performance may steadily use,
the quick three characters to describe. Steady is refers to the
system the stability (stability), a system must be able the normal
work, first to have to be stable, from the step leap response looked
should be restrains â–¡r is accuses the system system the accuracy, the
control precision, passes the commonly used static error to come
(Steady-state error) to describe, it expressed the system output
stable state value and the expected value difference of â–¡r quickly
are accuses the system system response the rapidity, passes the
commonly used rising time to come the quota description.
4th, PID control principle and characteristic
Is actual in the project, applies the most widespread
regulator control rule for the proportion, the integral, the
differential control, is called the PID control, also calls the PID
adjustment. The PID controller is published until now had the
nearly 70 years history, it by its structure simple, the stability is
good, the work may *, the adjustment convenience become one of
industry control main technical. When is controlled the object
the structure and the parameter cannot completely grasp, when or
cannot obtain the precise mathematical model, when the control theory
other technologies use with difficulty, the central controller
structure and the parameter must depend on * the experience and the
scene debugs determined that, by now applied the PID control
technology to be most convenient. Namely when we incompletely
understood a system and is controlled the object â–¡o or cannot when
obtains through the effective survey method the system parameter,
suitably comes in handy the PID control technology. The PID
control, is actual also has PI and the PD control. The PID
controller is according to the system error, using the proportion, the
integral, the differential gauge figures out the control quantity to
carry on the control.
The proportion (P) controls
The proportional control is one simplest control mode.
Its controller output and the loading error signal becomes the
proportion relations. When only has the proportional control
system output existence static error (Steady-state error).
The integral (I) controls
In the integral control, the controller output and the
loading error signal integral becomes the direct ratio relations.
To a automatic control system, if after enters the stable state
the existence static error, then called this control system has the
static error or the abbreviation has the difference system (System
with Steady-state Error). In order to eliminate the static
error, must introduce in the controller "accumulates the sub-item".
Accumulates the sub-item to be decided to the error by the time
integral, along with the time increase, accumulates the sub-item to be
able to increase. Thus, even if the error is very small,
accumulates the sub-item also to be able to enlarge along with the
time increase, it impels the controller the output to increase
ambassador the static error further to reduce, until is equal to zero.
Therefore, the proportion + integral (PI) the controller, may
cause the system after enters the stable state the non- static error.
The differential (D) controls
In the differential control, the controller output and
the loading error signal differential (namely erroneous rate of
change) becomes the direct ratio relations. The automatic
control system in overcomes erroneous in the adjustment process
possibly to be able to appear the vibration even to lose steadily.
Its reason is because exists has a bigger inertia module (link)
or has the lag (delay) the module, has the suppression error the
function, its change always falls behind the erroneous change.
Solution is causes the suppression error the function change "in
advance", namely approaches the zero hour at the error, the
suppression error function should be zero. This meant that,
introduces "the proportion" in the controller the item often is only
insufficient, a proportion function only is enlarges erroneous the
peak-to-peak value, but at present needs to increase is "the micro
sub-item", it can forecast the erroneous change the tendency, like
this, has the proportion + differential the controller, can cause the
suppression error the control action to be equal to zero ahead of
time, even is the negative value, thus avoided controlling the
quantity the serious over modulation. Therefore to has a bigger
inertia or the lag is controlled the object, the proportion +
differential (PD) the controller can improve the system in adjustment
process dynamic characteristic.
5th, PID controller parameter 整定
The PID controller parameter 整定 is the control
system design core content. It is according to is controlled the
process the characteristic to determine the PID controller the
scale-up factor, the integration time and the differential time size.
The PID controller parameter 整定 method are very many,
summarizes has two big kinds: One is the theoretical calculation
整定 law. It mainly is rests on the system the mathematical
model, the process theoretical calculation definite controller
parameter. This method obtained arrives the estimated data not
necessarily may straight take over the use of, but also must actually
carry on the adjustment and the revision through the project.
Two is the project 整定 method, it mainly relies on the
project experience, directly carries on in the control system
experiment, also the method simple, is easy to grasp, is actual in the
project is widely used. The PID controller parameter project
整定 method, mainly has the critical ratio method, the response tune
long-base method and fades the subtraction. Three methods
respectively have its characteristic, its common ground all is through
the experiment, then carries on according to the project empirical
formula to the controller parameter 整定. But regardless of
uses the controller parameter which which one method obtained arrives,
all needs to carry on the final adjustment and the consummation in the
actual movement. Now generally uses is the critical ratio
method. Carries on the PID controller parameter as follows using
this method 整定 the step: (1) first in advance chooses an
enough short sampling period to let the system work â–¡r (2) only join
the proportional control link, appears the threshold oscillation until
the system to the input step leap response, took down the by now
proportion magnification factor and the threshold oscillation cycle
â–¡r (3) in certain controls under the system to obtain the PID
controller through the formula computation the parameter. The
article originates from:
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